A Low-Power Delta-Modulation-Based ADC for Wearable Electrocardiogram Sensors

In this brief, a new ultra-low power analog-to-digital converter (ADC) based on delta (
${\Delta }$
)-modulation approach is presented for wearable Electrocardiogram (ECG) sensor systems. In the proposed structure, a voltage-to-time converter (VTC) is employed as the residue quantizer in
${\Delta }$
-modulation based ADC circuit. So, the requirement on the high-frequency sampling rate in such ADCs is relaxed and it can be realized with low-power consumption. This structure produces one-bit output data wherein the pulse-width of output data at every clock cycle is proportional to the input signal variation. Therefore, the output data rate is significantly reduced. The proposed ADC is designed in TSMC 0.18
${\mu }\text{m}$
CMOS technology and post-layout simulation results exhibit maximum 10.9 effective number of bits (ENOB) with 68.12 nW power from a 0.8 V power supply. This ADC circuit achieves a peak signal-to-noise and distortion ratio (SNDR) about 67.4 dB over ECG signal bandwidth with 4 kHz sampling frequency and occupies about 0.02 mm
²
silicon die area.